Compilare: user.cpp: In member function ‘void Problem::parse(const string&, int, int)’: user.cpp:60:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while ( end != string::npos ) ^ user.cpp:63:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if ( end != string::npos ) ^ user.cpp:81:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if ( index != string::npos ) ^ user.cpp:91:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if ( index != string::npos ) ^